During the formation of lockstitches which are formed by concatenating a needle thread around a bobbin thread, an undesirable effect is sometimes produced call haloing which has its results in producing uneven slack stitches particularly on the top side of the fabric as it is being sewn. It is believed that this effect is produced due to the frictional engagement of the work limb of the needle thread and the takeup limb between the casting off of the loop seized by the loop taker and the stitch setting operation. It is, of course, desirable in producing lockstitches that the stitches be relatively firmly and evenly set so as to firmly secure the plies of fabric being sewn without any undesirably slack thread appearing on the face of the fabric. In accordance with the present invention, this undesirable effect is substantially eliminated by providing a needle thread work limb retaining means which is disposed so as to seize the work limb of the needle thread substantially immediately after loop seizure by the beak of the loop taker. The work limb retainer means is positioned so as to keep the work limb separated from the take up limb of the needle thread during passage of the loop around the loop taker and is released therefrom after the thread loop has completed its passage about the loop taker. The take up limb may then be pulled up by the needle during its return stroke without any frictional engagement with the work limb to thereby set the stitch just formed without any excess thread from the work limb being pulled up through the fabric which might have caused a slack loop on the top side of the fabric. Thread detainers are known in the art for holding on to a thread loop after cast off for maintaining tension on the thread loop so as to prevent "pig tailing" which may be defined a twisting of the thread upon itself. This is a common defect in shuttles of the oscillating type and is not analogous to haloing. These thread detainers are disposed merely to hold on to the thread loop and do not act to separate the two limbs of the thread loop, namely the work limb and the take up limb, in order to prevent haloing. Further, such thread detainers are often mounted on the leading end of the usual thread guard or on the stationary bearing race frame in shuttle mechanisms.
As will be apparent from the following detailed description, a work limb thread retainer is provided which is supported apart from the loop taker and the bobbin in a position for substantially immediately seizing the work limb of the needle thread loop after it is seized by the beak of the loop taker. The work limb is retained by the retainer means during passage of the needle thread loop around the loop taker for concatenation with a thread from the bobbin case and is released after the thread loop has completed its passage about the loop taker. As mentioned above, the retainer serves to keep the work limb and the take up limb separated so that they do not come into frictional engagement during the cycle described above and thereby there is little, if any, chance of the take up limb frictionally engaging the work limb during the return stroke of the needle to thereby substantially prevent haloing. Other objects and advantages of the invention will be best understood when reading the following detailed description with the accompanying drawings.